Increased Prevalence of Filaggrin Deficiency in 51 Patients with Recessive X-Linked Ichthyosis Presenting for Dermatological Examination

X-linked ichthyosis (XLI) is a keratinization disorder caused by deficient activity of steroidsulfatase. In contrast, ichthyosis vulgaris is due to semidominant mutations of the filaggrin gene ( FLG ). In view of phenotypic variations of these ichthyoses we speculated that XLI may be influenced by additional FLG mutations in a significant number of patients. We characterized a group of 51 patients with XLI and systematically analyzed them for additional FLG mutations (R501X, 2282del4, R2447X, S3247X). The study was complemented by morphological analyses. Full FLG sequencing for rare mutations was performed in special cases. Interestingly, prevalence of FLG mutations was significantly increased compared to a population-based control cohort of 1,377 individuals (17.6% vs. 8.4%, p=0.038). Palmoplantar hyperlinearity was significantly associated with the FLG mutation status. Ichthyosis severity score seemed to be increased in XLI with FLG mutations, but the difference was not significant (p=0.124). To our surprise, percentages of atopic manifestations were highly prevalent in both subgroups, 40% and 33% in XLI without and with filaggrin deficiency, respectively. Of note, reduction of filaggrin staining or keratohyalin could not be explained by FLG mutations in all patients. However, we conclude that FLG mutations represent a significant genetic modifier of XLI. [196 words]